uniq command

The uniq command can eliminate or count duplicate lines in a presorted file. It reads in lines and compares the previous line to the current line. Depending on the options specified on the command line it may display only unique lines or one occurrence of repeated lines or both types of lines.  The common idiom is

sort | uniq  

and

sort | uniq -c

For example

grep 'hysteresis' * | awk -F: '{print $1}' | sort | uniq | wc -l  

or in more complex pipe:

cut -d '"' -f 2 $1 | cut -d '/' -f 3 | tr '[:upper:]' '[:lower:]' \
    | sort | uniq -c | sort -r > $1_sites

The default output is to display lines that only appear once and one copy of lines that appear more than once. It is also useful to filter out multiple blank lines from unsorted output of other commands. For example, the dircmp command displays its output using pr; thus the output usually scrolls off your screen before you can read it. But if you pipe the output of the dircmp command through the uniq command, the blank lines are reduced and the output is more compact.

Syntax

uniq [ -options [ input [output] ]

Options

Arguments

The following arguments may be passed to the uniqcommand.

NEWS CONTENTS

• 190317 : TTTT uniq ( TTTT uniq, )
• 190317 : Emulation of uniq Unix command in ksh93 - AIX Expert ( Emulation of uniq Unix command in ksh93 - AIX Expert, )
• 190317 : Perl reimplementation from Perl Power Tools ( Perl reimplementation from Perl Power Tools , )

Old News ;-)

TTTT uniq

uniq(1) takes a stream of lines and collapses adjacent duplicate lines into one copy of the lines. So if you had a file called foo that looked like:

---

davel
davel
davel
jeffy
jones
jeffy
mark
mark
mark
chuck
bonnie
chuck

---

You could run uniq on it like this:

---

% uniq foo
davel
jeffy
jones
jeffy
mark
chuck
bonnie
chuck

---

Notice that there are still two jeffy lines and two chuck lines. This is because the duplicates were not adjacent. To get a true unique list you have to make sure the stream is sorted:

---

% sort foo | uniq
jones
bonnie
davel
chuck
jeffy
mark

---

That gives you a truly unique list. However, it's also a useless use of uniq since sort(1) has an argument, -u to do this very common operation:

---

% sort -u foo
jones
bonnie
davel
chuck
jeffy
mark

---

That does exactly the same thing as "sort | uniq", but only takes one process instead of two.

uniq has other arguments that let it do more interesting mutilations on its input:

• -d tells uniq to eliminate all lines with only a single occurrence (delete unique lines), and print just one copy of repeated lines:

  ---

  % sort foo | uniq -d
  davel
  chuck
  jeffy
  mark
  

  ---

• -u tells uniq to eliminate all duplicated lines and show only those which appear once (only the unique lines):

  ---

  % sort foo | uniq -u
  jones
  bonnie
  

  ---

• -c tells uniq to count the occurrences of each line:

  ---

  % sort foo | uniq -c
     1 jones
     1 bonnie
     3 davel
     2 chuck
     2 jeffy
     3 mark
  

  ---

  I often pipe the output of "uniq -c" to "sort -n" (sort in numeric order) to get the list in order of frequency:

  ---

  % sort foo | uniq -c | sort -n
     1 jones
     1 bonnie
     2 chuck
     2 jeffy
     3 davel
     3 mark
  

  ---

• Finally, there are arguments to make uniq ignore leading characters and fields. See the man page for details.

---

Tuesday Tiny Techie Tip -- 03 December 1996

Emulation of uniq Unix command in ksh93 - AIX Expert

	#!/usr/bin/ksh93
################################################################
#### Program: uniq_k93
#### 
#### Description: Emulation of the Unix "uniq" command
#### 
#### Author: Dana French ([email protected])
####         Copyright 2004
#### 
#### Date: 07/22/2004
#### 
################################################################
function uniq_k93 {
  typeset TRUE="0"
  typeset FALSE="1"
  typeset OLDPREV=""
  typeset FNAME=""
  typeset STDIN="${1: ${FALSE}}"
  STDIN="${STDIN:-${TRUE}}"

  if (( STDIN == TRUE ))
  then
    getUniqLine_k93 OLDPREV
  else
    for FNAME in "${@}"
    do
      if [[ -f "${FNAME}" ]]
      then      
        exec 0<"${FNAME}"
          getUniqLine_k93 OLDPREV
        exec 0<&-
      else
        print -u 2 "ERROR: \"${FNAME}\" does not exist or is not a regular file."
      fi
    done
  fi
  return 0
}
################################################################
function getUniqLine_k93 {
  nameref OLDPREV="${1}"
  typeset PREV="${OLDPREV}"
  typeset CURR
  IFS=""

  [[ ${OLDPREV} = "_" ]] &&
    read -r -- PREV &&
    print -r -- "${PREV}"

  while read -r -- CURR
  do
    [[ "_${PREV}" = "_${CURR}" ]] && continue
    print -r -- "${CURR}"
    PREV="${CURR}"
  done
  OLDPREV="${PREV}"
  return 0
}
################################################################

uniq_k93 "${@}"

Perl reimplementation from Perl Power Tools

#!/usr/bin/perl -w
# uniq - report or filter out repeated lines in a file

use strict;

my $VERSION = '1.0';

END {
  close STDOUT || die "$0: can't close stdout: $!\n";
  $? = 1 if $? == 255;  # from die
}

sub help {
  print "$0 [-c | -d | -u] [-f fields] [-s chars] [input files]\n";
  exit 0;
}

sub version { print "$0 (Perl Power Tools) $VERSION\n"; exit 0; }

# options
my ($optc, $optd, $optf, $opts, $optu);

sub get_numeric_arg {
  # $_ contains current arg
  my ($argname, $desc, $opt) = @_;
  if    (length) { $opt = $_ }
  elsif (@ARGV)  { $opt = shift @ARGV }
  else           {die "$0: option requires an argument -- $argname\n"}
  $opt =~ /\D/ && die "$0: invalid number of $desc: `$opt'\n";  
  $opt;
}

while (@ARGV && $ARGV[0] =~ /^[-+]/) {
  local $_ = shift;
  /^-[h?]$/    && help();        # terminates
  /^-v$/       && version();     # terminates
  /^-c$/       && ($optc++, next);
  /^-d$/       && ($optd++, next);
  /^-u$/       && ($optu++, next);
  /^-(\d+)$/   && (($optf = $1), next);
  /^\+(\d+)$/  && (($opts = $1), next);
  s/^-f//      && (($optf = get_numeric_arg('f', 'fields to skip')), next);
  s/^-s//      && (($opts = get_numeric_arg('s', 'bytes to skip')), next);

  die "$0: invalid option -- $_\n";
}

my ($comp, $save_comp, $line, $save_line, $count, $eof);

# prime the pump
$comp = $line = <>;
exit 0 unless defined $line;
if ($optf) {($comp) = (split ' ', $comp, $optf+1)[$optf] }
if ($opts) { $comp  =  substr($comp, $opts) }

LINES: 
while (!$eof) {
  $save_line = $line;
  $save_comp = $comp;
  $count = 1;
 DUPS: 
  while (!($eof = eof())) {
    $comp = $line = <>;
    if ($optf) {($comp) = (split ' ', $comp, $optf+1)[$optf] }
    if ($opts) { $comp  =  substr($comp, $opts) }
    last DUPS if $comp ne $save_comp;
    ++$count;
  }
  # when we get here, $save_line is the first occurrence of a sequence
  # of duplicate lines, $count is the number of times it appears
  if    ($optc) { printf "%7d $save_line", $count }
  elsif ($optd) { print $save_line if $count >  1 }
  elsif ($optu) { print $save_line if $count == 1 }
  else          { print $save_line }
}

exit 0;

__END__

=head1 NAME 

uniq - report or filter out repeated lines in a file

=head1 SYNOPSIS

uniq [B<-c> | B<-d> | B<-u>] [B<-f> I] [B<-s> I] [I]

=head1 DESCRIPTION

The uniq utility reads the standard input comparing adjacent lines and
writes a copy of each unique input line to the standard output.  The sec-
ond and succeeding copies of identical adjacent input lines are not writ-
ten.  Repeated lines in the input will not be detected if they are not
adjacent, so it may be necessary to sort the files first.

The following options are available:

=over

=item c

Precede each output line with the count of the number of times the
line occurred in the input, followed by a single space.

= item d

Don't output lines that are not repeated in the input.

=item f I

Ignore the first fields in each input line when doing compar-
isons.  A field is a string of non-blank characters separated
from adjacent fields by blanks.  Field numbers are one based,
i.e. the first field is field one.

=item s I

Ignore the first chars characters in each input line when doing
comparisons.  If specified in conjunction with the B<-f> option, the
first chars characters after the first fields fields will be ig-
nored.  Character numbers are one based, i.e. the first character is
character one.

=item u

Don't output lines that are repeated in the input.

=back

If additional arguments are specified on the command line, they are
used as the names of input files.

The uniq utility exits 0 on success or >0 if an error occurred.

=head1 COMPATIBILITY

The historic B<->I and B<+>I options are supported as
synonyms for B<-f> I and B<-s> I, respectively.

This version accepts 0 as a valid argument for the B<-f> and
B<-s> switches; some implementations of uniq do not.

=head1 SEE ALSO

sort(1)

=head1 BUGS

I has no known bugs.

=head1 AUTHOR

The Perl implementation of I was written by Jonathan Feinberg,
I.

=head1 COPYRIGHT and LICENSE

This program is copyright (c) Jonathan Feinberg 1999.

This program is free and open software. You may use, modify, distribute,
and sell this program (and any modified variants) in any way you wish,
provided you do not restrict others from doing the same.

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uniq

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Created: May 16, 1997; Last modified: March 12, 2019